Process of cooling reduced metallic material in carbonaceous gases



06L 1957 R. E. KUSNER EFAL PROCESS OF COOLING REDUCED METALLIC MATERIAL IN CARBONACEOUS GASES Filed March 6, 1956 HI m m Y 008 E TU N M M W W n ITK A RR E w m 6 l M E v. w B M0 F E 0R 0U 2T A R E P M WE T 0 m %OZ4S 8MQMFH%&M%%%&M 8 4 0 642086 2 86 M.@9%9%9%888877M7W66M O Un t d w s Pa o PROCESS OF COOLING REDUCED METALLIC MATERIAL IN CARBONACEOUS GASES Robert Ernest Kusner andEdwin Pope Kawasaki, Cleveland, Ohio, assignors toRepublic Steel Corporation, Cleveland, Ohio, a corporation of New Jersey Application March 6, 1956, Serial No. 569,859

Claims. c1. 75-5 The present invention relates to' a process of cooling reduced metallic material in carbonaceous gases, and particularly to such a process employed at the termination of a reduction operation on this material and in which the final product does not have its carbon content increased to an objectionable point, i. e. over about 0.1% (by weight) carbon by reason of the carbonaceous character of the gases present. 7

In the art of preparing metallic powder, particularly for use in powder metallurgy operations, it is now com mon to reduce compounds of one or more of the constituents of the powder from their respective oxidized states or positive valance states to their respective elemental states. For example, iron in the form of oxide, chloride or some other reducible compound is reduced to metallic iron by being maintained in a reducing atmosphere and at a relatively high temperature. Similarly, other metal compounds may be reduced and also mixtures of compounds of different metals and/or some of the metals in a metallic state may be simultaneously reduced to provide reduced metallic bodies which are usable as, and/or can be comminuted to form, metallic powders. It is common to effect such reduction with hydrogen. If the reduction is accomplished using substantially pure hydrogen, with more or less water vapor present therein, but without the simultaneous presence of carbonaceous gases such as carbon monoxide, carbon dioxide and/0r hydrocarbons, there is no substantial problem requiring resort to the presentinvention. Even when the reduction proper is effected at a temperature of 1500 F. or more and in the presence of some carbonaceous gases, the breaking down of the carbonaceous very hard and difiicult to press. Irrespective of Whether or not this theory is correct, however, it is found that if the deposition of carbon is prevented during the cooling of the metal following the reduction thereof, in accordance with the present invention, this hardening of the metal is avoided. It has further been found that in instances where carbon is desired in the final article, it may be added after the metal is cold without resulting in hardening the metal powder in an undesired manner; and that the pressing of iron powder mixed in the cold with carbon in some form is substantially the same as the pressing of carbon-free iron powder. A clear distinction must be made, therefore, between carbon deposited in or on the metallic material during the cooling, which is undesired, and carbon mixed with the completely cooled metallic powder, which is often desired and deliberately resorted to.

As aforesaid, if hydrogen alone were present during this cooling down,'so that there were no carbonaceous gases present which could be decomposed to deposit carbon, there would be no problem. However, pure hydrogen and/ or reducing gases free of any carbonaceous constituents are substantially more expensive than is a gas which may contain an adequate amount of hydrogen, but'which also contains more or less carbonaceous constituents. Such carbonaceous gases containing an ample amount of hydrogen are cheaply available in large constituents of these gases at and above this relatively high temperature to deposit carbon on or in the reduced or reducing material is so slow as not to introduce any substantial problem.

It has been found, however, that if gases containing carbonaceous constituents as aforesaid are used during the cooling down period of the reduced material, following the reduction thereof, and in the temperature range from about 1500 F. to about 800 F., there is a very substantial tendency for some or all of the carbonaceous materials to break down, depositing carbon in or on the reduced material, which is objectionable at this stage of the operation. It has been found that the presence of substantial amounts of carbon in the powder make it quite difiicult to press, so as to obtain a pressed product (green pressed part) havinga sufiiciently high bulk density without using excessive pressing pressure.

quantities, as coke oven gas and as surplus gas from oil refineries having platinum refining operations (sometimes known as platformer gas). Water gas also is a very cheap gas containing hydrogen, but also containing a substantial amount of carbon monoxide. There are, of course, many other commercial gases in this general category which are relatively cheap as compared with gases containing substantial amounts of hydrogen, but free of carbonaceous constitutents.

It has further been found that When the total of the carbonaceous constituents of the make-up gas expressd as a percentage of the total of these constituents plus hydrogen is not over about 7%, the tendency for breaking down of the carbonaceous constituents to deposit carbon is not sufficiently serious that it need give any real concern. Hence in such gases also the present invention is not necessary. The use of such low carbonaceous content gases is to be considered outside the purview of the present invention. On the other hand, it has been found that there must be at least about as much hydrogen as the total of all the carbonaceous gases; that the hydrocarbons, if present, must be mostly saturated as hereinafter set forth and correspond generally to the formula CnH2n+2, in which n has an average value of not over about 3.

' The total of unsaturated hydrocarbons which may be present without introducing or causing undesirable results has been found to be about 4% as a maximum value. Under these circumstances and when using some relatively inexpensive gas during this critical cooling period, the present invention comes into effect.

In accordance with this invention it has been found that if a sufficient water vapor content is maintained in the gases about the material as it cools, considered as a ratio of water vapor to hydrogen, then the deposition of carbon to the extent of permanently increasing the carbon content of the solidmaterial above a desired minimum is effectively prevented. More particularly, the water vapor content should be maintained at a sufliciently highlevel to approach, but not substantially to exceed that amount which is in equilibrium with hydrogen in accordance with the reaction:

This equilibrium amount of water vapor is a function of temperature and decreases as the temperature decreases. It is found generally that if the water vapor content is too far below this equilibrium amount at any given temperatureand in the presence of carbonaceous gases, carbon will be deposited in anundesired manner. If on the other hand the water vapor content exceeds the equilibrium amount, the oxidation of some iron, which is present according to the present invention, will ensue. The commercial art has developed a practical limit as to the amount of iron in oxide form which they will accept. This limit is defined by what is termed hydrogen loss, which means the percentage loss in weight of a sample of metal powder in question heated in hydrogen at 2000" F. plus or minus 15 F. for one hour. The limit which has become accepted in the commercial powder metallurgy industry is 1 /2 as a maximum tolerable hydrogen loss on this basis. It is desired, of course, that the hydrogen loss in fact be kept substantially less than that, preferably less than 1%.

The invention will be better understood by reference to the accompaying drawing, in which:

The single figure is a graph showing the equilibrium concentration of water vapor expressed as a ratio by volume or by mol of hydrogen to water vapor plotted against temperature.

It will be noted that as the temperature decreases, the percentage of hydrogen divided by the percentage of water vapor which is tolerable to prevent oxidation of the iron correspondingly increases. In other words for a substantially given hydrogen content, the tolerable amount of water vapor decreases. Thus the desired zone of operation is above and to the right of the equilibrium line as seen in the drawing. It may be, however, that in a given operation the actual conditions will be a short distance on the wrong side of this equilibrium line for short periods. This is tolerable as long as the total amount of iron oxidized during these periods is not too great, so as to give a hydrogen loss to the final product which exceeds tolerable limits as aforesaid.

The starting material supplied to the reducing zone for the reduction proper may be of any composition As to the limitations on the constituents of the carbonaceous gases, it has been found that carbon monoxide, carbon dioxide and the lower saturated hydrocarbons are the ones with which we are particularly concerned, namely, hydrocarbons having the formula:

CnH2n+2 in which n has an average value of not over about 3.

' In this connection, it is meant that there may be some which is desired, for example, to be supplied to the process of the Crowley United States Patent No. 2,744,002, issued May 1, 1956, or it may be a mixture of different metals or their compounds, so as to yield a final product which contains more than one metal and which may, for example, simulate an alloy steel in its overall chemical composition. In any event, the present invention is applicable where the reduced metallic material, i. e. the reduced material present at the termination of the reduction operation proper, consists predominantly of iron and may consist essentially of iron. The present invention is equally applicable irrespective of whether the reduction proper took place partly or wholly in the presence of a hydrogen halide, such as gaseous hydrogen chloride in addition to hydrogen and/or whether the reducing gas used did or did not contain any carbonaceous gases as herein defined. The present invention relates primarily to the cooling of the reduced material from the relatively high temperature at which the material is reduced and specifically from about 1500 F. down to a temperature of not over about 800 F. It is in this range that the deposition of carbon is critical, as above about 1500" F. as aforesaid, carbonaceous gases do not appear to break down to deposit carbon; or if they do, that carbon is almost immediately reconverted to some gaseous form, possibly carbon monoxide. On the other hand, below about 800 F., the rate at which carbonaceous gases break down is so slow that the deposition or carbon does not present a real problem.

methane, some ethane, propane and possibly some higher hydrocarbons, including butane, etc. However, when the proportions of the various hydrocarbons are considered, including methane, in which n equals 1, ethane, in which n equals 2, etc. and an average value of n is calculated considering all the hydrocarbons present and their respective values of n, then the only gases which are really appropriate are those in which this average value of "11 is not over about 3. Thus the presence of relatively smaller amounts of saturated hydrocarbons having n=4 or more, such as butane, etc., are not precluded.

Another limitation on this gas is that it must not contain more than about 4% of unsaturated hydrocarbons as these types of material will cause difiiculties when present in greater proportions. Thus either an excess of unsaturated hydrocarbons over about 4% or the presence of hydrocarbons as aforesaid where n has a value greater than about 3 will result in some carbon being deposited in the metal during cooling, with the undesirable result-s hereinabove described.

A further limitation on the gas is that there must be at least as much hydrogen as the total of all the carbonaceous gases present. Furthermore, as aforesaid, where the total of the carbonaceous gases as defined above is less than 7% of the total of these gases plus hydrogen, no substantial difficulties are encountered, so that this is a further limitation on the applicability of the present process.

Within all these limitations, therefore, the process is necessary and is of peculiar utility in coping with a very real problem encountered in the commercial manufacture of ferrous powders for use in powder metallury. It has been found, for example, that when a platformer" gas originating as above set out is available, this gas may be and has been used on a substantial commercial scale. The platformer gas which has been successfully employed comprises as an average analysis: 83.8% hydrogen, 6.1% CH4, 4.3% C2Hs, 3.2% CsHs, 1.5% C4H10, 0.4% C5H12 and 0.7% of similar saturated hydrocarbons where n is over 5 (all percentages being by volume). When this gas is used as an original gas and as make-up gas in a recycling system as taught, for example, in the application of Crowley U. S. patent aforesaid and also in the application of Hatcher et 211., Serial No. 457,963,

filed September 23, 1954, then the average composition of the recycled gas as supplied to the reducing zone and the gas which is present during the cooling of the reduced material is about 79% hydrogen, 9% carbon monoxide, 1% carbon dioxide, and 11% hydrocarbons (as aforesaid), in addition to the water vapor present.

As will be noted from the foregoing, the amount of water vapor which is both tolerable and desired at a relatively high temperature is substantially greater than the amount of water vapor in the gases which is tolerable and desired at a much lower temperature. As such, therefore, it becomes necessary to adjust downwardly the water vapor content of the gases as the material is cooled. This may be done progressively or in predetermined increments. One practical way is to readjust the water vapor content in the gases as the materials cool past each F. mark in their average temperature as indicated by a thermocouple or other temperature indicating apparatus positioned to be sensitive to the temperature of the solid materials during their cooling. If desired, the 'water vapor concentration may be controlled automatically by suitable means not herein particularlydescribed or illustrated in response to variations in the temperature of the material being cooled. The provision of such means per se' forms no necessary part of the present invention. I

The invention will be better understood by a consideration of the following examples:

EXAMPLE I Thisexample illustrates the practice of the process of the present invention in cooling a reduced material consisting essentially of iron from about 1500 F. to about 750 F. The average analysis of the recycled gas supplied to and through the reducing and cooling zone during the cooling (on a dry basis) and with the percentages given referring to volume percentages is: hydrogen 85.0%, Cog-0.8%, CO-3.8%, and hydrocarbons (as aforesaid) 10.4%. During this-cooling cycle the percentages of water vapor present, calculated on the basis of a ratio to the hydrogen present by volume, were adiusted for different temperature .ranges, the adjustment being made at approximately each 100 F. of temperature drop and to a point corresponding generally to the maximum permissible water vapor content at the lower temperature limit in each temperature zone. The values for the water vapor actually used are given in Table 1 which follows:

l The figure given represents the approximate equilibrium value for the ratio of H20 to hydrogen by volume at the lower limit of each temperature range respectively on the basis that the gas used is 85% hydrogen.

The procedure set out in this example resulted in an ironpowder containing 0.014% carbon, which is much better (lower in carbon) than the maximum tolerable amount of carbon in accordance with present industrial practice in this respect as set out hereinabove.

EXAMPLE n The purpose of this example is to illustrate the eifect upon the carbon content of the cooled material of different compositions of gas used as make-up gas in a recycle system as above referred to.

First, it is believed desirable to set out a theory which is presently believed to be correct as to the mechanism of the breakdown reaction resulting in the deposition of carbon. It is believed that this is particularly due to the reaction.

The carbon monoxide in the gas is 'believe'd'to a certain extent at least to be introduced by the breakdown of hydrocarbons as follows:

I Table 2 which follows shows how the COand CO2 content'of the recycle gas varies (based on experimental -'tests) with different percentages .of hydrocarbon gases (Cal-lean) in the makekup gas. 3

It is believed that the high value of 3.6 for the CO2 is probably due to experimental error as itseems out of line. In general, the carbon dioxide content of the gases rose to a maximum in the order of magnitudeof 2 to 2.5, but did not substantially exceed this maximum notwithstanding a large increase in hydrocarbon gases and in the CO content of the recycled gases. p

A considerable number of experimental tests where made including a first group in which the gases used-as make-up gas had a concentration of about 93% H2 and 7% hydrocarbons, which corresponded generally to the formula CzHs. Substantially no trouble was encountered from this gas during all tests, which were conducted in a manner generally simulating commercial operation; although it was found that if the cooling time was extended 50% or more beyond the normal cooling time corresponding to commercial operation, trouble was encountered due to an excessively high carbon content in the finished product.

A second group of tests was made using a make-up gas having (apart from water vapor) 88% Hz,,7% CH4 and 5% CsHa. 'Here again no difficulty was experienced when following the teachings of the present invention, but the water vapor content was required to be closer to the equilibrium line shown in the accompanying drawing than in the case of the gas containing 93% hydrogen.

A third group of tests was made using a make-up gas analyzing (in addition to water vapor) 83% H2, 11% CH4 and 6% CaHs. 'The result indicated the same trends above discussed, with a still narrower, but still entirely adequate, operating range above and to the right as seen in the accompanying drawing of the equilibrium line.

When, however, butane (C4H1o) was substituted for propane (CaHs), the permissible or operative range was found to be much narrower. Thus, with a gas having 83 H2, 11% CH4 and 6% C4H1o, the hydrogen to water ratio must be maintained between the limits of 88:12 at 1500 F. down to 96:4 at 800 R, which is much narrower than the corresponding limits required for lighter average bydrocarbons.

When the percentage of higher hydrocarbons, such as butane, was substantially raised to 12% and 16% respectively, the percentage of carbon in the finished products rose to undesired values, indicating that the limit of n=3 as above set out is a practical outside limit for the hydrocarbons in the gases which can be used, while obtaining desirable results by following the process of the present invention.

EXAMPLE III A further series of tests was run to determine the proportions of hydrocarbon gases (of a composition as aforesaid) which was tolerable without having the carbon content in the cooled material excessively high. In these tests, makeup gases having 70%, 60%, 50% and 40% hydrogen were used in successive tests with the balance respectively hydrocarbon (principally methane and a minor proportion of propane) in each instance. It was found that as the percentage of hydrogen in the gases was reduced, the operating range, i. e. the limit for successful operating practice, upward and to the right of the equilibrium line as shown in the accompany drawing, tends more closely to approach that line; and that when a gas consisting essentially of 40% hydrogen, 38.6% methane and 21.4% propane was used, the resulting metal powder 7 had a carbon content of 0.017% and a hydrogen loss of 1.07%, which lead to the conclusion that the tolerable limit had been exceeded and that there should be at least as much hydrogen as the total of carbonaceous gases present.

EXAMPLE IV The purpose of the tests set out in this example is to demonstrate the limit set out in this case for unsaturated hydrocarbons which may be present in the gas, and still produce a tolerably good or acceptable product.

A first test run was made in a S-pound (rated) capacity reducing unit provided with means for recycling gases through the reducing zone and means for augmenting the recycled gases by make-up gas and for bleeding out some gas as well as for condensing water from recycled gas, all substantially as taught in the Crowley Patent No. 2,744,002 and in the Hatcher et al. application Serial No. 457,963, both aforesaid. In this run the raw material was what is known to the applicants as Old Bed Superconcentrate, which is a concentrate made by magnetic separation between magnetite (FesO4) and gangue, the concentrate as prepared containing less than 1% gangue and substantially all the remainder, magnetite, and this material being pelletized prior to its introduction into the reduction unit. The gas supplied initially and as make-up gas to the recycling system had a composition of 55% hydrogen, 41% methane and 4% ethylene. To this there was added during the reduction per se 1%% gaseous hydrogen chloride. Gas samples were taken of the recycled gas during the cool-down period, #1 at the start, #2 about halfway through, and #3 at the end. The analyses of these recycled gas samples were as follows:

The resulting iron powder had a hydrogen loss of 1.13% and a carbon content of 0.080%, both of which were considered quite high, but the powder was usable in powder metallurgy and had good strength and shrinkage, even through it was quite hard. These conditions, therefore, were deemed to represent substantially the maximum permissible concentration of unsaturated hydrocarbons (ethylene).

In a second test run in the same apparatus an oxidized mill scale was used. Mill scale as it is originally received is principally FezOa and also contains smaller amounts of the oxides of steel-alloying metals such as nickel and molybdenum. The particular mill scale used contained about 1% NiO and about A% molybdenum in the form of M003 (each calculated as metal). Prior to the reduction of this material, it is subjected to an oxidizing roast, so as to convert any oxides of iron other than FezOs to that ratio of iron to oxygen. This practice seems to have a desirable effect in connection with the subsequent reduction operation in reducing the iron to a metallic state. This material also was pelletized prior to being placed in the reducing unit; and in this test 2.38 pounds of pellets were reduced in the test made. The reduction was effected using a coke-oven gas as a reducing agent, the gas having the following composition:

During the reduction there was added to this gas 1.5% hydrogen chloride gas. The operation was conducted otherwise as set forth in respect to the first test in this example. The resulting product had a hydrogen loss of 0.45% and a carbon content of 0.103%. This again represents about the maximum tolerable carbon content from a practical commercial point of view.

A third run using pellets of Old Bed Superconcentrate prepared as aforesaid and the same coke-oven gas as above described gave a product having a hydrogen loss of 1.00% and a carbon content of 0.106%, again indicating that with this type raw material as distinguished from the mill scale, substantially the same results are obtained. Thus the carbon content of the final product seems to be a function of the gases used, rather than a result of using different types of raw material.

EXAMPLE V This example as well as the second one hereinabove reported in Example IV illustrates the application of the process to an alloyed powder as distinguished from substantially pure iron. In this example, as in the test included in Example IV above, mill scale was employed as the raw material, the mill scale having the composition given above. In this test the mill scale was pelleti zed using an agglomerate consisting of organic material which is completely burned out and removed during the reducing operation. A 700-pound batch of mill scale pellets prepared as aforesaid was first oxidized by an oxidizing roast (which served to burn out the carbon of the organic binder used as well as to convert any lower oxide of iron to the form of FezOa). Then it was reduced with a gas having an initial composition of 83% hydrogen, 10% CH4 and 7% CaHa, this gas being used as the initially supplied gas and as the make-up gas. To. this gas, during the reduction operation proper, there was added about 3% gaseous hydrogen chloride, the hydrogen chloride being discontinued, however, prior to the cooling down operation forming the principal part of the process of the present invention. The resulting alloyed powder had a hydrogen loss of 0.29% and a carbon content of 0.012% and was found to be very satisfactory in all its properties for use in making powdered metal parts by powder metallurgy operations.

The principles of the present invention have been set forth hereinabove along with the limitations within which the invention is believed to be operative, the reasons for these limitations and the preferred conditions for obtaining maximum desirable results in each of many phases of the invention. Other equivalents may reasonably occur to those skilled in the art from the foregoing teachings. We do not wish to be limited, therefore, except by the scope of the appended claims, which are to be construed validly as broadly as the state of the art permits.

What is claimed is:

1. In the making of a metallic powder, which consists predominantly of iron, by the reduction of at least one metallic constituent thereof at a relatively high temperature, and in which the reduced material is thereafter cooled from the temperature of reduction to a temperature less than about 800 F. in the presence of a gas, which contains hydrogen and also contains at least one carbonaceous gaseous material selected from the group consisting of carbon monoxide, carbon dioxide and saturated hydrocarbons having the formula CnH2n+2, in which n has an average value of not over about 3, and which gas contains not more than about 4% of unsaturated hydrocarbons, there being at least as much hydrogen as the total of all carbonaceous gases present, and in which said carbonaceous gases are present to the extent of at least about 7% by volume of the total of said carbonaceous gases plus hydrogen; the process which, comprises the step of substantially preventing the deposition of carbon on and in contact with the reduced metallic material, so that the latter when cooled will have a carbon content of not over 0.1% (by weight), by maintaining in the gaseous atmosphere in contact with the reduced material during and throughout the cooling thereof a water vapor content having a sufficiently high ratio of HzOzHz, so as substantially to prevent said deposition of carbon, but not sufficiently high to convert a substantial amount of the metallic iron present to iron oxide, so that the hydrogen loss of the reduced and cooled material will not exceed 1 /z%.

2. In the making of a metallic powder, which consists predominantly of iron, by the reduction of at least one metallic constituent thereof at a relatively high temperature, and in which the reduced material is thereafter cooled from the temperature of reduction to a temperature less than about 800 F. in the presence of a gas, which contains hydrogen and also contains at least one carbonaceous gaseous material selected from the group consisting of carbon monoxide, carbon dioxide and saturated hydrocarbons having the formula cnH2n+2, in which n has an average value of not over about 3, and which gas contains not more than about 4% of unsaturated hydrocarbons, there being at least as much hydrogen as the total of all carbonaceous gases present; and in which said carbonaceous gases are present to the extent of at least about 7% by volume of the total of said carbonaceous gases plus hydrogen; the process which comprises the step of substantially preventing the deposition of carbon on and in contact with the reduced metallic material, so that the latter when cooled will have a carbon content of not over 0.1% (by weight), by maintaining in the gaseous atmosphere in contact with the reduced material during and throughout the cooling thereof a water 10 vapor content, which approaches in its H2O:H2 ratio but does not substantially exceed that amount which is in equilibrium with hydrogen in the reaction:

said Water vapor content being adjusted downward as the material is cooled and as the equilibrium amount aforesaid decreases with decreasing temperature, so that the hydrogen loss of the reduced and cooled material will not exceed 1% 3. The process according to claim 2, in which the water vapor content in the gaseous material in contact with the reduced material during the cooling thereof to a temperature less than 800 F. is progressively varied as the material cools, so that the final product will have a carbon content of not over about 0.05%.

4. The process according to claim 2, in which the metallic material being cooled consists essentially of iron.

5. The process according to claim 2, in which the gas in contact with the solid material during the cooling thereof to a temperature of not over 800 F. consists essentially (apart from water vapor) of hydrogen 79%, carbon monoxide 9%, carbon dioxide 1%, and saturated hydrocarbons as aforesaid 11%.

References Cited in the file of this patent UNITED STATES PATENTS 1,097,156 Alford May 19, 1914 1,758,786 Ekelund May 13, 1930 2,282,144 Fahrenwald May 5, 1942 2,609,288 Stuart Sept. 2, 1952 

1. IN THE MAKING OF A METALLIC POWDER, WHICH CONSISTS PREDOMINANTLY OF IRON, BY THE REDUCTIONOF AT LEAST ONE METALLIC CONSISTITUENT THEREOF AT A RELATIVELY HIGH TEMPERATURE, AND IN WHICH THE REDUCED MATERIAL IS THEREAFTER COOLED FROM THE TEMPERATURE OF REDUCTION TO A TEMPERATURE LESS THAN ABOUT 800*F. IN THE PRESENCE OF A GAS, WHICH CONTAINS HYDROGEN AND ALSO CONTAINS AT LEAST ONE CARBONACEOUS GASEOUS MATERIAL SELECTED FROM THE GROUP CONSISTING OF CARBON MONOXIDE, CARBON DIOXIDE AND SATURATED HYDROCARBONS HAVING THE FORMULA CNH2N+2, IN WHICH "N" HAS AN AVERAGE VALUE OF NOT OVER ABOUT 3, AND WHICH GAS CONTAINS NOT MORE THAN ABOUT 4% OF UNSATURATED HYDROCARBONS, THERE BEING AT LEAST AS MUCH HYDROGEN AS THE TOTAL OF ALL CARBONACEOUS GASES PRESENT, AND IN WHICH SAID CARBANACEOUS GASES ARE PRESENT TO THE EXTENT OF AT LEAST ABOUT 7% BY VOLUME OF THE TOTAL OF SAID CARBONACEOUS GASES PLUS HYDROGEN; THE PROCESS WHICH COMPRISES THE STEP OF SUBSTANTIALLY PREVENTING THE DEPOSITION OF CARBON ON AND IN CONTACT WITH THE REDUCED METALLIC MATERIAL, SO THAT THE LATTER WHEN COOLED WILL HAVE A CARBON CONTENT OF NOT OVER 0.1% (BY WEIGHT), BY MAINTAINING IN THE GASEOUS ATMOSPHERE IN CONTACT WITH THE REDUCED MATERIAL DURING AND THROUGHOUT THE COOLING THEREOF A WATER VAPOR CONTENT HAVING A SUFFICIENTLY HIGH RATIO OF H2O:H2, SO AS SUBSTANTIALLY TO PREVENT SAID DEPOSITION OF CARBON, BUT NOT SUFFICIENTLY HIGH TO CONVERT A SUBSTANTIAL AMOUNT OF THE METALLIC IRON PRESENT TO IRON OXIDE, SO THAT THE HYDROGEN LOSS OF THE REDUCED AND COOLED MATERIAL WILL NOT EXCEED 11/2%. 